Key Steps In The Investment Castings Process

The investment casting process begins with fabrication of a sacrificial pattern of the same basic geometrical shape as the intended finished cast part. Patterns are normally made of investment casting wax that is injected into a metal wax injection die (Fig. 1).

Fig. 1 Wax Injection

Once a wax pattern is produced, it is assembled with other wax components on a central wax stick, called a sprue, to form a casting cluster or assembly (Fig. 2).

Fig. 2. Assembly.

The entire wax assembly is then dipped in a ceramic slurry and covered with a sand stucco (Fig. 3), and allowed to dry.

Fig. 3. Shell Building

The dipping and stuccoing process is repeated until a shell of ~6-8 mm (1/4-3/8 in) is applied. Once the ceramic has dried, the entire assembly is placed in a steam autoclave to remove most of the wax.  The remaining amount of wax soaked into the ceramic shell is burned out in a furnace (Fig. 4).

Fig. 4. Dewax

At this point, all of the residual pattern and gating material is removed, and the ceramic mold remains. The mold is then preheated to a specific temperature and filled with molten metal, creating the metal casting (Fig. 5).

Fig. 5. Metal Casting Pouring

Once the casting has cooled sufficiently, the mold shell is chipped away from the casting (Fig. 6).

Fig. 6. Knockout

Next, the gates and runners are cut from the casting (Fig. 7).

Fig. 7. CutOff

After minor final post processing (sandblasting, machining), the castings - identical to the original wax patterns - are complete and ready for shipment (Fig. 8).

Fig. 8 Finished Casting